Dry Air and Cool Waters’ Affects on Hurricane Season

Dry air and cool sea surface temperatures: two ingredients that can really weaken the genesis and intensification of tropical cyclones. The environmental conditions over the Atlantic Ocean have been rather hostile as of late. The main basis of these storms are thunderstorms, and with dry air in place, it inhibits their development. Thus,d ry air has a negative impact on tropical storms or hurricanes because it chokes off the development of convection.

This time of the year, there are often these large plumes of dry air that move from Africa toward the Atlantic Ocean. These plumes, often known as Saharan Air Layers, can promote downdrafts around the thunderstorms of a developing tropical cyclone, enhancing wind shear, which is another inhibitor of development. According to NOAA, these Saharan Air Layers are most common during “late spring, summer, and early fall and usually move out over the tropical North Atlantic Ocean every 3-5 days.”

The below MODIS satellite image captured on Monday highlights the most recent Saharan Air Layers. Notice how expansive this is. A couple times per year, these dry air outbreaks can even travel as far west as the Gulf of Mexico, which can make for beautiful sunrises and sunsets due to the added particulates in the air.

MODIS Satellite Image from Monday, June 4th, 2018

Another inhibitor of tropical cyclone development and intensity is cool sea surface temperatures. The Atlantic Ocean is unusually cool relative to average, especially in the region where tropical cyclones form, known as the Main Development Region. This area, referred to as the MDR, is where numerous — and sometimes the most intense — tropical cyclones form during the peak of hurricane season. This area encompasses most of the Caribbean Sea and the area between the Lesser Antilles and the western coast of Africa. In the image below, notice how the blue color shoes dominate this area as well as parts of the southwestern Atlantic. This means that sea surface temperatures are below average. To the north, near the Eastern Seaboard, water temperatures are actually warmer than normal due to a dominant high pressure of the region. However, this area is not a common region for origins of tropical systems, so the warmer water temperatures won’t likely help in the formation of a tropical cyclone. That being said, if a cyclone passes through the area, these temperatures could be key in strengthening it rather than weakening it, as the region usually does.

Current Sea Surface Temperatures | Credit: Tropical Tidbits

Since the start of May, the North Atlantic overall has been running below-average following warmer than normal temperatures as a whole during much of April. Tropical cyclones gain much of their energy from the warm ocean waters. Without the warmth, it is more difficult for cyclones to form.

Numerous forecasting outlets that predict how many storms will form during hurricane season have had to lower their forecast numbers due to the cool Atlantic Ocean temperatures. They believe this will inhibit the number of named storms that form this year, as well as the number of hurricanes and major hurricanes. There aren’t many signs that suggest the Atlantic will warm to above-average anytime soon.

Jackson is Head of Content at WeatherOptics and produces several forecasts and manages all social media platforms. Previously, Jackson forecasted local weather for southwestern Connecticut, founding his website, Jackson's Weather, in the March of 2015. He is currently studying Meteorology and Broadcast Journalism at the University of Miami.